Cast elements in UIElementCollection to Type of respective element

January 28, 2022

In an wpf-Application I want to cast the child elements of a Panel to the respective elements Type.
For example, a UIElementCollection has 3 children:
TextBox
Button
Label

If I iterate the UIElementCollection I’ll get an UIElement and have to cast every element to it’s Type before I can work with it.

So I tried to use a generic method, that will cast the UIElement to it’s real type:

public static T getCastTo<T>(UIElement ele)
{                       
     return (T) (object) ele;
              
}

Using it by invoking

TextBox tb = SomeGenerics.getCastTo<TextBox>(ele);

gives me a TextBox as expected.

What I now want to do is using it in a loop something like

foreach(UIElement ele in uielementCollection) {
    SomeGenerics.getCastTo<ele.GetType()>(ele);  // or
    SomeGenerics.getCastTo<typeof(ele)>(ele);
}

but the compiler tells me that I can’t use a variable as a Type.
Is there a way to use the generic method without specifying the Type "manually"?

>Solution :

Just use Enumerable.Cast(hard cast) or Enumerable.OfType(also filters):

IEnumerable<TextBox> allTextBoxes = uielementCollection.OfType<TextBox>();

In general you can’t use a generic methods if you know the type at runtime, generics are a compile time feature. So all you can do is to cast them to the desired type or the common base type. Then you can process them somewhere else by try-casting them to a specifiy type:

foreach (Control c in uielementCollection)
{
    switch (c)
    {
        case TextBox txt:
            // handle TextBox
            break;

        case Label lbl:
            // handle Label
            break;
        //  ... and so on
    }
}